Packet writing

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Packet writing is a technique of writing ("burning") on optical media in a manner that is common to hard drives or floppy disks. This is also known as "incremental writing".

technology

Normally, optical media such as CD- R ( W ) and DVD ± R (W) can only be written to in one piece ( disc-at-once , track-at-once and session-at-once ).

The term “packet writing” refers to a technique for the incremental writing of optical media. This makes it possible to use optical media such as a hard disk or a floppy disk . Files can thus be copied, moved, changed, renamed or deleted on the respective optical medium.

The “ Universal Disk Format ” (UDF) version 1.50 or higher is used as the file system for packet writing . UDF is best adapted to the requirements of optical media and is therefore the recommended file system on all incrementally written optical media.

To use packet writing, you need a CD / DVD drive that supports writing data in small units on the medium. Almost all CD and DVD burners support this function, but it could be the case that it is missing, especially on older devices.

UDF

UDF stands for "Universal Disk Format" and describes the file system (or high-level formatting ) in which the data or files are written to the medium. UDF was developed with special attention to optical storage media.

For an optical medium, every write access is a burden. Different optical media withstand different amounts of such loads, and this at every point in the entire storage area. In order to keep the service life of the medium as long as possible, it is therefore necessary to load it as evenly as possible.

Universal disk format version 1.50 or higher is required for use with packet writing. UDF version 1.02 is a static file system, comparable to ISO 9660 , which is used, for example, as an "ISO / UDF bridge" for DVD-Video .

One of the most common burdens when writing to optical media is updating the table of contents. Every time a file changes, even if it is just the file name, that change must be written to the table of contents. UDF version 1.50 or higher is so well suited for packet writing because it stores the table of contents in different places on the optical medium and thus distributes the load.

Another problem is the management of free storage space. Files are simply written to hard drives where there is no other file - in other words, where, for example, a file has just been deleted and there is free space again. On optical media, however, this would mean that memory area that has already been used (because it has been written to) is charged again (because it is written to again). UDF versions 1.50 and higher therefore keep a list of areas which have already been described and how often these have been described. When a new file is saved in such a UDF file system, it is done at a point that has not yet been loaded or has not been loaded as often, the total load on the optical medium is thus kept roughly the same at all points.

UDF also offers a defect management system that hides already used (overloaded, destroyed) sections of the originally available storage space. Despite these failed areas, the optical medium can still be used. The use of this defect management depends on the software that implements the UDF file system.

Warning: Deleted or overwritten files are initially only marked as deleted in the UDF table of contents. This also applies if the file was deleted using special " eraser software". Reconstructing recently deleted files is therefore possible with relatively little effort. If it were absolutely necessary to physically delete a file from the respective medium, the entire memory area would have to be overwritten with new data, or the eraser program used can deal with the special features of the UDF file system.

For technical reasons, it is not possible to delete or overwrite anything that has already been written on media that can only be written to once (CD-R and DVD ± R). Therefore, once the medium is full, it can only be read, but no longer written to. Files deleted on such media are always relatively easy to reconstruct.

Important: Rewritable media can only guarantee a certain number of write accesses. Only the UDF file system in version 1.50 or higher loads the medium evenly so that these write accesses do not ruin the medium prematurely.

Packet writing is not UDF

Often no distinction is made between UDF and packet writing. Since this can lead to considerable confusion, the following should clarify how packet writing interacts with UDF, but also what makes the two fundamentally different.

What is UDF and what is its use?

  • UDF is a file system such as FAT32 , NTFS or ext3 .
  • A storage medium, a partition or similar (such as a loop device or a virtual drive ) can be formatted with UDF.
    In theory, it is also possible to format a partition on the hard drive with UDF. Although this is also practicable, it usually fails because of the support from the operating system.
  • UDF is available in different versions .
    However, the difference between UDF 1.02 and UDF 1.50 is as great as, for example, the difference between FAT32 (as in Windows 98 / Me) and NTFS (as in Windows 2000 / XP).
  • UDF is an ISO standard and is therefore at least partially supported by many operating systems.
    Most operating systems can read UDF versions 1.02, 1.50 and / or 2.01. Some operating systems can also write UDF (≙ full UDF support).

What is packet writing and how is it used?

  • Packet writing is a technique for writing to optical media in units of small packets, hence the name “packet” - small packets, and “writing” - to describe (burn onto the optical medium).
  • Packet writing is only possible with suitable hardware. However, almost all modern CD and DVD drives offer this hardware support.
  • Packet writing is understood as a driver, such as an ATAPI driver, which enables access to an ATAPI CD-ROM drive. The packet writing driver enables access to the medium in the manner described: small packets can be read and written, similar to how the sectors can be read and written on hard disks .
    • This means that packet writing works independently of the file system used. You can therefore format a medium that has been integrated into an operating system via the packet writing driver with any file system. In practice, however, this is not very advisable, with some operating systems even the packet writing driver prevents the use of file systems other than UDF.
    • For example, you could even put NTFS on an optical medium. However, we strongly advise against this, as the service life of the medium would be drastically reduced. One of the reasons for this is that NTFS is a journaling file system and initiates many write accesses with every file operation, which would put an extreme load on an optical medium. The same applies, for example, to ext3, as well as to all other journaling file systems, since they were primarily developed for hard drives.
    • Simple file systems such as FAT, FAT32 or ext2 (with the noatime mount option) only place a limited load on an optical medium, but always write the table of contents in the same place. These file systems are therefore only suitable to a limited extent for packet writing and optical media, but can be used in exceptional cases (e.g. for compatibility with older operating systems that do not yet support UDF). In general, however, it is also not advisable to use these file systems, since here too the service life of the optical medium decreases drastically with every write access.
  • Not all media require packet writing. For writing to DVD-RAM and BD-RE media, for example, the logic integrated in the DVD-RAM and Blu-Ray drive takes on the functionality that the packet writing driver provides as software for CD and DVD media . The implementation in the hardware enables better data security for the DVD-RAM standard and its successor BD-RE, since all write accesses are checked regardless of the operating system used and, if necessary, a defective sector is recognized and identified (defect management). In addition, the DVD-RAM medium offers clearly recognizable sectorization and a unique high rewritability of approx. 100,000 write accesses.
    For comparison: CD-RW media can withstand approx. 1,000 write accesses, but defective areas are only recognized during the next read process (which does not succeed or delivers incorrect data). This can be reduced by means of defect management implemented in the software, which, however, also reduces the writing speed on the respective medium (roughly halved).
    BD-RE media are now only designed for 1,000 writes, but special media trimmed for 10,000 writes are available.
  • Not all drives require packet writing. The " Mount Rainier (MRW) " standard stipulates that CD-R (W) and DVD ± R (W) media such as DVD-RAMs are also supported on the hardware side and can be used like hard drives or floppy disks.
    Theoretically. In practice, the operating system has to support this standard with an MRW driver in order for it to work. The advantage of Mount-Rainier in the hardware compared to packet writing (with UDF) in the software is obvious: the hardware regulates the defect management transparently in the background, defective sectors are recognized and masked out while writing, which means that the Data security increased. Furthermore, the MRW drive logic uses the UDF file system internally, but allows the user to use any file system. Nevertheless, one should not use a write-intensive file system, since every write process causes the medium to age.
    Note: Some packet writing programs also retrofit MRW support for the respective operating system. MRW read programs also exist which can at least read media written on MRW drives in non-MRW drives.
Info bulb.png For better illustration:
  • The packet writing driver accesses the drive using the CD / DVD hardware driver,
  • while the UDF driver, which is a file system driver, accesses the drive using the packet writing driver.

UDF and packet writing drivers (illustration)

software

To be able to use packet writing, you either need a driver or a packet writing program. These first make the packet writing function available in the operating system or the user. In order to be able to use the usual UDF file system, a UDF driver is also required. With some operating systems, these two functions (packet writing and UDF) are implemented in a single driver. Packet writing programs integrate both functions in one program.

Once the operating system has been prepared and the drivers installed, for example, optical media can first be formatted and then used like a hard disk in the usual way in the operating system.

The following is an incomplete list of drivers and packet writing programs for various operating systems.

GNU / Linux

  • pktcdvd is integrated in the current Linux kernel version 2.6
  • udffs has been integrated since Linux kernel 2.4

Mac OS

  • SAI WriteUDF! UDF Writer for Mac OS (Software Architects, Inc.)

Windows

  • B's CLiP (BHA Corporation)
  • DLA: Drive Letter Access (Sonic Solutions)
  • Drag-to-Disc, formerly DirectCD (Roxio, formerly Adaptec)
  • DVD Write Now - Freeware
  • Nero InCD (Nero AG, formerly Ahead)
  • SAI WriteDVD! and ReadDVD! (Software Architects, Inc.)
  • from Windows Vista integrated under the name live file system

Embedded

  • TinyUDF (StorageLabs BV)

Free "UDF reader" programs that only allow reading of UDF file systems:

  • B's CLiP UDF Reader / MRW Remapper, version 5.02
    reading support up to UDF version 1.50 for Windows 95 OSR2 / 98 / Me
  • B's CLiP UDF NT Reader, Version 1.00
    Reading support up to UDF Version 1.50 for Windows NT 4.0 SP6
  • Nero InCD Reader, Version 5: Reading support up to UDF-2.60 for Windows 2000 / XP / 2003 / Vista (32-bit) and Version 4:
    Reading support up to UDF version 2.60 for Windows 98 / Me / 2000 / XP / 2003
  • Veritas DLA UDF Reader, Version 2.55 from IBM (MIGR-42199)
    Reading support (UDF version unknown) for Windows 95/98 / 98SE / Me / NT / 2000 / XP
    Under "File link" the file b91z06us.exewith the description Veritas DLA UDF reader Download     (German) .

Web links

  • UDF specifications (English), edited by the O ptical S torage T echnology A ssociation (OSTA)

Individual evidence

  1. ↑ DVD Write Now
  2. ↑ StorageLabs TinyUDF Library 2.50
  3. ↑ B's CLiP UDF Reader / MRW Remapper, Version 5.02 ( Memento from December 10, 2008 in the Internet Archive )
  4. ↑ B's CLiP UDF NT Reader, Version 1.00 ( Memento from December 10, 2008 in the Internet Archive )
  5. ^ Veritas DLA UDF reader